An inherent problem in the production of metallic thin films is minimizing the electro-migration that occurs in the metal interconnects. The electro-migration results in the transport of metal material of an interconnect line, and is caused when free electrons dislodge the atoms of the conductive material upon the current density increase that occurs due to smaller cross-sectional dimensions of the interconnect lines. The electro-migration occurs due to the transfer of momentum from the electrons flowing in a metal conductor when the conductor fails, because of a void or break in the conductor. This phenomenon is generally known as an “electron wind.” The failure occurs most often along the grains of the conductive material since the atoms are not as firmly bound along the grains, and the grains provide efficient paths for the electron transport. These grains may extend in a direction which is parallel to the direction of the interconnect lines, i.e., along the direction of the current flow, which is considered to be particularly undesirable (i.e., such grain direction results in an increased electro-migration). If vacancies or voids are formed in the conductive material, the void that is formed reduces the cross-sectional area in a region of the interconnect through which the current may flow, effectively raising the current density of that region of the interconnect even further. Therefore, the void may become so large that an open circuit or a break in the interconnect line results. Alternatively, the atoms of the conducting material that are dislodged may accumulate in a region of the interconnect so as to form a protrusion. If the protrusion becomes large enough, a contact with an adjacent interconnect may occur, thereby causing an undesired connection between the adjacent interconnect lines.
As the features of integrated semiconductor circuit chips are reduced, the cross-section of the metal interconnect lines on the integrated circuit chips are also reduced. This decrease in the cross-sectional dimensions increases the current density in the interconnect lines, which creates increased electro-migration in the metal interconnects. Moreover, the electro-migration would likely increase with a presence of a random orientation of the microstructure of the thin film. Since increasing the grain size to be larger than the metallization line width and preparing semiconductor films with a uniform orientation would reduce the propensity for electro-migration failure, there is a need for a system and method to control crystallization, and produce thin films with the substantially uniform orientation of the microstructure of the thin film.
Control over the thin film microstructure may be obtained through the use of sequential lateral solidification (“SLS”) techniques. For example, U.S. Pat. No. 6,322,625 (the “'625 application”), U.S. patent application Ser. Nos. 60/239,194 (the “'194 application”), Ser. No. 09/390,535 (the “'535 application”), Ser. No. 09/390,537 (the “'537 application”), Ser. No. 60/253,256 (the “'256 application”), Ser. No. 09/526,585 (the “'585 application”) and International Patent Application Nos. PCT/US01/31391 and PCT/US01/12799, the entire disclosures of which are hereby incorporated herein by reference, describe advantageous apparatus and methods for growing large grained polycrystalline or single crystal structures using energy-controllable laser pulses and small-scale translation of a sample to implement the SLS techniques. As described in these patent documents, at least portions of the semiconductor film on a substrate are irradiated with a suitable radiation pulse to completely or partially melt such portions of the film throughout their thickness. In this manner, when the molten semiconductor material solidifies, a crystalline structure grows into the solidifying portions from selected areas of the semiconductor film which did not undergo a complete melting. Thereafter, the beam pulses irradiate slightly offset from the crystallized areas so that the grain structure extends into the molten areas from the crystallized areas. With the SLS techniques, and the systems described therein, crystallization may be controlled to modify the microstructure of the thin film (e.g., by creating larger grains, single-crystal regions, grain-boundary-location-controlled microstructures), and produce grains with a particular orientation.